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A Clear View of a Cloudy Brown Dwarf Companion from High-Resolution Spectroscopy
arXiv - PHYS - Solar and Stellar Astrophysics Pub Date : 2022-08-02 , DOI: arxiv-2208.01657
Jerry W. Xuan, Jason Wang, Jean-Baptiste Ruffio, Heather Knutson, Dimitri Mawet, Paul Mollière, Jared Kolecki, Arthur Vigan, Sagnick Mukherjee, Nicole Wallack, Ji Wang, Ashley Baker, Randall Bartos, Geoffrey A. Blake, Charlotte Z. Bond, Marta Bryan, Benjamin Calvin, Sylvain Cetre, Mark Chun, Jacques-Robert Delorme, Greg Doppmann, Daniel Echeverri, Luke Finnerty, Michael P. Fitzgerald, Katelyn Horstman, Julie Inglis, Nemanja Jovanovic, Ronald López, Emily Martin, Evan Morris, Jacklyn Pezzato, Sam Ragland, Bin Ren, Garreth Ruane, Ben Sappey, Tobias Schofield, Andrew Skemer, Taylor Venenciano, J. Kent Wallace, Peter Wizinowich

Direct imaging studies have mainly used low-resolution spectroscopy ($R\sim20-100$) to study the atmospheres of giant exoplanets and brown dwarf companions, but the presence of clouds has often led to degeneracies in the retrieved atmospheric abundances (e.g. C/O, metallicity). This precludes clear insights into the formation mechanisms of these companions. The Keck Planet Imager and Characterizer (KPIC) uses adaptive optics and single-mode fibers to transport light into NIRSPEC ($R\sim35,000$ in $K$ band), and aims to address these challenges with high-resolution spectroscopy. Using an atmospheric retrieval framework based on petitRADTRANS, we analyze KPIC high-resolution spectrum ($2.29-2.49~\mu$m) and archival low-resolution spectrum ($1-2.2~\mu$m) of the benchmark brown dwarf HD 4747 B ($m=67.2\pm1.8~M_{\rm{Jup}}$, $a=10.0\pm0.2$ au, $T_{\rm eff}\approx1400$ K). We find that our measured C/O and metallicity for the companion from the KPIC high-resolution spectrum agree with that of its host star within $1-2\sigma$. The retrieved parameters from the $K$ band high-resolution spectrum are also independent of our choice of cloud model. In contrast, the retrieved parameters from the low-resolution spectrum are highly sensitive to our chosen cloud model. Finally, we detect CO, H$_2$O, and CH$_4$ (volume mixing ratio of log(CH$_4$)=$-4.82\pm0.23$) in this L/T transition companion with the KPIC data. The relative molecular abundances allow us to constrain the degree of chemical disequilibrium in the atmosphere of HD 4747 B, and infer a vertical diffusion coefficient that is at the upper limit predicted from mixing length theory.

中文翻译:

从高分辨率光谱中清晰地看到多云的褐矮星伴星

直接成像研究主要使用低分辨率光谱($R\sim20-100$)来研究巨型系外行星和褐矮星伴星的大气,但云的存在常常导致所检索到的大气丰度(例如 C/ O,金属丰度)。这排除了对这些同伴形成机制的清晰见解。Keck Planet Imager and Characterizer (KPIC) 使用自适应光学器件和单模光纤将光传输到 NIRSPEC($K$ 波段 $R\sim35,000$),旨在通过高分辨率光谱解决这些挑战。使用基于 petitRADTRANS 的大气反演框架,我们分析了基准褐矮星 HD 4747 B 的 KPIC 高分辨率光谱 ($2.29-2.49~\mu$m) 和存档低分辨率光谱 ($1-2.2~\mu$m) ($m=67.2\pm1.8~M_{\rm{Jup}}$, $a=10.0\pm0.2$ au, $T_{\rm 有效}\约 1400$ K)。我们发现,我们测量的 KPIC 高分辨率光谱中伴星的 C/O 和金属丰度与其主星的一致,在 $1-2\sigma$ 内。从 $K$ 波段高分辨率光谱中检索到的参数也与我们选择的云模型无关。相比之下,从低分辨率光谱中检索到的参数对我们选择的云模型高度敏感。最后,我们在这个 L/T 转换伴星中用 KPIC 数据检测 CO、H$_2$O 和 CH$_4$(log(CH$_4$)=$-4.82\pm0.23$ 的体积混合比) . 相对分子丰度使我们能够限制 HD 4747 B 大气中化学不平衡的程度,并推断出垂直扩散系数处于混合长度理论预测的上限。我们发现,我们测量的 KPIC 高分辨率光谱中伴星的 C/O 和金属丰度与其主星的一致,在 $1-2\sigma$ 内。从 $K$ 波段高分辨率光谱中检索到的参数也与我们选择的云模型无关。相比之下,从低分辨率光谱中检索到的参数对我们选择的云模型高度敏感。最后,我们在这个 L/T 转换伴星中用 KPIC 数据检测 CO、H$_2$O 和 CH$_4$(log(CH$_4$)=$-4.82\pm0.23$ 的体积混合比) . 相对分子丰度使我们能够限制 HD 4747 B 大气中化学不平衡的程度,并推断出垂直扩散系数,该系数处于混合长度理论预测的上限。我们发现,我们测量的 KPIC 高分辨率光谱中伴星的 C/O 和金属丰度与其主星的一致,在 $1-2\sigma$ 内。从 $K$ 波段高分辨率光谱中检索到的参数也与我们选择的云模型无关。相比之下,从低分辨率光谱中检索到的参数对我们选择的云模型高度敏感。最后,我们在这个 L/T 转换伴星中用 KPIC 数据检测 CO、H$_2$O 和 CH$_4$(log(CH$_4$)=$-4.82\pm0.23$ 的体积混合比) . 相对分子丰度使我们能够限制 HD 4747 B 大气中化学不平衡的程度,并推断出垂直扩散系数处于混合长度理论预测的上限。
更新日期:2022-08-04
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